linux-kernel - Re: [PATCH] printk: use this_cpu_{read|write} api on printk

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Message-ID: <1290790791.2855.259.camel@edumazet-laptop>
Date:	Fri, 26 Nov 2010 17:59:51 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, heiko.carstens@...ibm.com,
	tglx@...utronix.de, mingo@...e.hu
Subject: Re: [PATCH] printk: use this_cpu_{read|write} api on printk_pending

Le vendredi 26 novembre 2010 à 10:40 -0600, Christoph Lameter a écrit :

> This only works if printk_needs_cpu is always passed the current cpu. The
> check for cpu_is_offline suggests that the function is also used for other
> cpus. The __this_cpu_read() will then get the printk_pending stat for the
> current cpu and not for the specified cpu.
> 
> 

I guess you read the changelog too fast ;)

I posted this patch after noticing printk_needs_cpu() was always used
for the current cpu.

We have other functions around, that always work for the current cpu.

We pass cpu as a parameter, mostly because smp_processor_id() was a bit
expensive in old kernels, and is still expensive because of sanity
tests.

Now we have this_cpu_ api, we probably can do a cleanup to avoid now
useless parameter passing.

If we had this_cpu_is_online() function, we could avoid (int cpu) param
in printk_needs_cpu()



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